[reasonisfaith]

The ability to do work.

[spunkets]

"No, matter is not energy. It is the speed of light squared, divided by energy. ...This concept is very basic."

It's divided by what energy? What does the energy represent?

"The ability to do work.

No. For instance, you can not do work with a proton. The energy is what the particle itself consists of. In this case, it represents the rest mass of the particle, m_o. One can not do work with the particle unless the particle is destroyed, or a reaction occurs between particles that causes a release of energy. The particle's mass is then reduced in an amount equal to the energy released. The energy then ends up as other particles, or an increase in some product particle's mass.

The equation is E=m_oc². The speed of light can be assigned a value of one. Then it's clear that the particle's rest mass is equal to it's energy.